I have always really liked iCam [iTunes link]. It will certainly be on my 'best iPhone apps of the year' list. Now it's been updated to automatically record video when it detects motion, and it allows you to play it back on your iPhone.
This was a much requested feature, and in my testing it worked like a champ. iCam can use almost any webcam to monitor a location. I use my built-in camera on my MacBook Pro, and a Linksys wireless webcam to monitor my pet bird. I can set either camera to send an alert if they detect motion, and now, with the new feature, the software takes a very quick succession of stills (several images per second) that I can view right from my iPhone wherever I may be. You just hit the play button and you can see what or who set off the recording.
You can remotely turn on the image recording, and even the motion detection notifications. All this in a U.S. $4.99 app. To make it all work you'll need some software running on your PC or Mac, and that software is free for the downloading. If you have the cameras, iCam makes for a complete and low cost home security system. Setup does not require any firewall tinkering. It just works.
You can monitor up to 4 webcams, and see them all simultaneously on your iPhone. To get everything up and running you'll need an iPhone or iPod touch with OS 3.0 or above, the iCam app, and iCam Source for your home computer. The software runs on Windows XP/Vista/7 or OS X 10.4 or later. Here's a link to a video so you can see how it works.
Just the thing to keep track of the house/kids/pets over the holidays, or any time.